4. Playing Levels, Modes and Styles

Sigma Chess supports a wide range of playing modes and levels, which are all set from the Level menu. There are 11 main groups (modes) of playing levels - to be described shortly - which can be selected in the Level Dialog (which is opened via the Playing Mode & Level... command from the Level menu) shown below:

The Level Dialog

Additionally, there are some special options that work in conjunction with some of the playing levels. Finally, Sigma Chess supports five different playing styles. The playing levels and styles can only be changed when it is your turn to move. Changing playing mode and/or levels will reset the chess clocks.

The actual level is indicated next to the chess clocks. For the Tournament and Normal levels, the number of moves left to the next time control is shown. Additionally, the icon for the current playing mode is shown next to the chess clock of the side to move.

The Normal Level

In these levels each side has to play the specified number of moves within a given time limit. The time limit and the number of moves are set independently in the Time and Moves popup menus. Initially, Sigma Chess starts up in blitz mode, i.e. 5 minutes per player for all moves.

During a game, when/if the specified number of moves have been played, the player in question receives a new time budget. For example, with 30 minutes to 40 moves, each player will receive an extra 30 minutes on the clock once the first 40 moves have been played, and another 30 minutes after move 80 etc. If a player runs out of time before having performed the necessary number of moves, that player loses on time. The game can be continued, though.

The Tournament Levels

The Tournament mode lets you customize three successive time controls: The primary, secondary and tertiary controls. A time control is defined by a time budget for white and black and the number of moves to play within this time control. If a player runs out of time before having played the indicated number of moves, he loses on time. Once a player reaches the specified number of moves, he passes on to the next time control and the available time on his clock is increased by the amount specified for the new time control. Note, that all the remaining moves have to be played in the last (tertiary) time control.

For example, in a tournament game, each player might be given 2 hours for the first 40 moves, 1 hour for the next 30 moves and half an hour for all the remaining moves.

The Average Levels

Here you simply define the average time per move (for Sigma Chess). There are 10 predefined levels ranging from 5 seconds per move up to 2.5 minutes per move.

The Leisure Level

In this level you decide how much time to spend per move as the game goes by. Sigma Chess will then try to keep up with your time usage. This level is ideal if you do not want to feel tyrannized by your chess clock.

The Fixed Depth Levels

Sigma Chess will search until its full width search depth (the one shown in the display) reaches the specified maximum. Sigma Chess supports a maximum search depth of 50 half moves (plies).

The Novice Levels

If you are a beginner you can use one of the eight novice levels. Sigma Chess will apply a one ply search and will make occasional blunders. The endgame databases are bypassed in these levels.

The Infinite Level

Here Sigma Chess will search "infinitely", unless it finds a forced mate, reaches its maximum search depth of 50 half moves or is stopped by you. The opening library is bypassed in this level.

The Solver Level

Here Sigma Chess will search until it finds a move exceeding the specified score and time limit.

The Mate Finder Levels

Sigma Chess uses a specialized search algorithm for solving mate problems. First you specify the (maximum) number of moves to mate, and then you invoke the mate finder via the Go command.

If no mate is found, a dialog appears stating this. If a mate is found, you will be given the option of either canceling the mate search, continuing the search for alternative solutions (called cooks) or accepting the solution. If you accept the solution, Sigma Chess will play the move (called the key) and decrease the mate level by one. This way you can play through the mate sequence move by move.

The Monitor Level

Sigma Chess won't perform any moves on the board, but it will continually search in the background as you manually play or undo moves on the board (not available in the Lite version).

The Manual Level

In this playing mode Sigma Chess will not start thinking after you have performed a move. This way you can use the program as an ordinary chess board. If you invoke the Go command, Sigma Chess will start thinking, but it will not perform any moves on the board once it completes the analysis.

Permanent Brain

This option only applies to the time controlled levels (the first 4 playing modes). Normally, Sigma Chess will also think when it is your turn to move, by trying to predict your next move. If you play this predicted move, Sigma Chess can save valuable time on its own chess clock. When the Permanent Brain option is off, Sigma Chess will not think on your time, which reduces the playing strength somewhat.

Non deterministic

When Sigma Chess is not playing moves from the opening library, its behavior is, in theory, completely deterministic: in a given position it will always play the same move under the same conditions (i.e. same playing level/mode/style, time left on the clock, transposition table size etc.). However, in practice when using the time-based levels Sigma Chess will in some cases play different moves, particularly if it is thinking on the opponent's time, because here the outcome of the search also depends on how much time you spend in certain positions. For the fixed depth and analysis levels, Sigma Chess is however, deterministic.

If you turn on the Non deterministic option, Sigma Chess will not always choose the same move under identical conditions. This of course does not imply that it will pick its moves at random, but rather that it will "randomize" between equally strong moves. Note that this option has no effect on the Mate Finder.

Playing Styles

Sigma Chess supports five different playing styles incarnating different kinds of temperament in terms of attack and defense. The default style is Normal which is also the objectively strongest style, where Sigma Chess is neither overly aggressive nor too defensive. In the Aggressive style, Sigma Chess will concentrate more on attack of the opponent king than on defense of its own king. Conversely, the Defensive style focuses more on defense than on attack.

The two remaining playing styles represent opposite extremes regarding attack and defense and are mainly intended for fun. In the Desperado style, Sigma Chess will concentrate only on attacking the opponent king, resulting in wild and entertaining games. Finally, in the Chicken style, Sigma Chess will place its main emphasis on defending its own king by driving away any attacks.